The effect of {O, N} = X ••• M = {Ti, Zr, Hf } interactions on the sensitivity of C-NO2 trigger bonds in FOX-7: Approach based on the QTAIM/EDA-NOCV analysis

The local chemical reactivity of FOX-7 (1,1-diamino-2,2-nitroethylene, also known as DADNE from DiAmino-DiNitroEthylene) was elucidated through a quantitative study of the electrostatic potential on the molecular surface, topological analysis based on Bader's theory, and the EDA-NOCV method. Unlike (O2N)(2)C=C(NH2)-H2N center dot center dot center dot Cp2MCH3+ complexes, which exhibit both sigma-donor and pi-acceptor features, the situation is different concerning the (H2N)(2)C=C(NO2)-(O)NO center dot center dot center dot Cp2MCH3+ complexes, where both charge transfers correspond to the sigma-donation. The two charge transfers reinforce each other, resulting in increased stability for (H2N)(2)C=C(NO2)-(O)NO center dot center dot center dot Cp-2 MCH3+. This seems to strengthen the (H2N)(2)C=C(NO2)-(O)NO center dot center dot center dot M={Ti,Zr,Hf} bond, which may explain the high stability of (H2N)(2)C=C(NO2)-(O)NO center dot center dot center dot Cp2MCH3+ compared to (O2N)(2)C=C(NH2)-H2N center dot center dot center dot Cp2MCH3+. Results from topological analysis revealed that the decreased sensitivity to decomposition of C-NO2 bonds depends on the chemical nature of the interacting metal, and the best achievements are obtained for the Hf-based complex. Our results demonstrate that the interaction of M = {Ti, Zr, Hf } with C-NO2 is more favourable than that with C-NH2, this specific action on the trigger bond may support the use of Metallocene Methyl Cations (MMC) as possible neutralisers.